In the field of industrial machines having fixed and movable members, bushings, sleeves and shoe assemblies are well known and commonly used in industry.
U.S. Pat. No. 5,624,695 entitled Securing Assembly For Injection Molding Machines issued on Apr. 29, 1997 to Husky Injection Molding Systems Ltd. and discloses a platen securing assembly. A stationary platen and moving platen are interconnected through a plurality of tie bar members. The tie bar members are supported and guided by a guide shoe located between the tie bar members and moving platen. The guide shoe is a fixed solid block of material and includes an integral wearing surface.
U.S. Pat. No. 5,275,550 entitled Hydromechanic Mold Clamping Mechanism issued to Industries Romi S.A., Brazil on Jan. 4, 1994 and discloses a hydromechancial clamp for injection molding machines. Two fixed platens are interconnected by a plurality of tie bar members. A moving platen is located intermediate the fixed platens and the tie bar members pass through the moving platen. A fixed solid bushing is disposed between an opening in the moving platen and the cylindrical surface of the tie bar member. The fixed solid bushing runs the entire width of the moving platen.
U.S. Pat. No. 5,135,385 entitled Clamping System issued to Ube Industries Ltd., on Aug. 4, 1992 and discloses a clamping system. A fixed platen and moving platen are interconnected by a plurality of tie bar members. A fixed solid bushing is disposed between an opening in the moving platen and the cylindrical surface of the tie bar member. The fixed solid bushing runs the entire width of the moving platen.
U.S. Pat. No. 5,238,394 entitled Mold Clamping Apparatus For Molding Apparatus issued to Nissei Jushi Kogyo K.K. on Aug. 24, 1993 and discloses a clamping apparatus. A fixed platen and moving platen are interconnected by a plurality of tie bar members. A fixed solid bushing is disposed between an opening in the moving platen and the cylindrical surface of the tie bar member. The fixed solid bushing runs the entire width of the moving platen.
U.S. Pat. No. 4,874,309 entitled Die Clamping Apparatus issued to Mitsubishi Jukogyo Kabushiki on Oct. 17, 1989 and discloses a die clamp. A fixed platen and moving platen are interconnected by a plurality of tie bar members. The moving platen has a plurality of openings for passing each tie bar member through the moving platen without a bushing, wear pad, or shoe assembly. The tie bar member slides on a ram insert located in each opening of the moving platen.
U.S. Pat. No. 4,304,540 entitled Hydraulic Press issued on Dec. 8, 1981 to Carl K. Hammon and discloses a hydraulic press including a fixed solid wedge guide mechanism. The wedge guide mechanism includes a wedge shoe adjustably mounted on a movable platen. The wedge shoe carries a removable solid wear plate that slides along an elongated solid wear plate.
U.S. Pat. No. 5,137,443 entitled Apparatus For Forming Hollow Plastic Article issued on Aug. 11, 1992 to Husky Injection Molding Systems and discloses a blow molding machine. A pair of long fixed "T" shaped solid wear strips are attached on opposing sides of a pallet. The wear strips communicate with a pair of "T" shaped recesses in the channel track for reciprocal movement of the pallet with respect to the channel track.
U.S. Pat. No. 5,885,458 entitled Wear Strip Assembly For Use In A Waste Water Treatment Facility issued On Mar. 23, 1999 to United States Filter Corporation and discloses a wear strip assembly for use in a waste water treatment facility. Long rigid "C" shaped wear strips are secured to a concrete floor through a number of anchor plates. Rigid "L" shaped wear shoes are secured to a flight through a rectangular upright portion. The wear shoes include a rectangular horizontal surface in contact with the wear strips. The rectangular horizontal surface slides over the wear strip during reciprocal movement of the flight in a horizontal direction.
U.S. Pat. No. 5,785,486 entitled Replaceable Wear System issued on Jul. 28, 1998 to McNeilus Truck and Manufacturing Corporation and discloses a replaceable wear system for use in refuse packing or ejecting mechanism. In one arrangement, a long rigid wear pad is substantially rectangular in cross section and includes a lengthwise triangular recess formed in the bottom of the wear pad for sliding engagement on a complimentary triangular rail located on a frame. In another arrangement, a long rigid wear pad is substantially triangular in cross section with a surface formed on the hypotenuse for sliding engagement on a complimentary wear surface located on the frame. The wear pads are retained with the packing arm through recesses for holding the wear pads and plates for securing the ends of the wear pads with the packing arm. The wear pads slide over the wear surfaces during reciprocal movement of the packing ram in a horizontal direction.
U.S. Pat. No. 5,560,713 entitled Ejector Wear Shoe issued on Oct. 1, 1996 to McNeilus Truck and Manufacturing Corporation and discloses a replaceable wear shoe for use on the ejection or packing mechanisms of a refuse hauling truck. A long rigid wear shoe is "C" shaped in cross section forming an inner channel. A rigid "T" shaped (cross section) slide bar communicates with the inner channel allowing smooth operation. The wear shoe slides over the slide bar during reciprocal movement of the receptacle.
The prior art devices are prone to several deficiencies and problems. For example, the fixed solid guide shoe of U.S. Pat. No. 5,624,695 has high compression loads at a peripheral edge of the wearing surface resulting in excessive wear and relatively early failure due to uneven loads.
The fixed solid bushings of U.S. Pat. Nos. 5,275,550, 5,135,385, and 5,238,394 require tight machining tolerances to press fit the bushing into the opening in the moving platen and to receive the cylindrical tie bar member. Alignment is critical and any misalignment of this device may cause early bushing failure. Replacement of the device requires considerable time and equipment.
The prior art devices are static and cannot compensate for differing loads, non-uniform loads, bending moments, and stress profiles over the wearing surface.. They are relatively expensive. Assembly of the machine and wear pads requires considerable time for lateral and longitudinal alignment of the components. The components tend to be long for maintaining alignment.
Early or frequent failure of wear pads leads to maintenance problems and is undesirable for machine down time and associated costs to disassemble the machine, replace the components, and re-assemble the machine.
Therefore, it is desirable to provide a shoe assembly and wearing surface which overcomes the aforedescribed problems of the prior art devices. There is a need for improving the wear characteristics of a wearing surface extending the useful life of a wear pad.